I have one that I converted. I really like it. First of all there is a series of people you can use for the conversion. You can purchase the parts and get special weapons to do the conversion as well if you are afraid of cutting on a very expensive weapon. Here is the low down
Mag conversion are the special weapons conversions from top notch. They involve a bold carrier key replacement as well as a gas piston, mag well, and a few other random items. You have to make a cut in the SL8 receiver at the mag well to allow the AR mag to go in. This is pretty simple with a dremel (I never used one before that day and it worked good) and then a polishing bit for the touch up.
The Stock I got was the Special Weapons clone. It is a little longer but allows for removal of the pin after the ban drops and firing from a folded mag. You can also pop a C lenth stock on this if you are not interested in firing folded. This is also simple only requiring the moving of the parts in the trigger housing.
The barrel work was done by Larry at Area 51 guns. He will cut the barrel to any length and put any attachment on it (provided it is legal). I have seen his K and C conversions for those that have the SBR stamp. Personally, I went with a 14.5 inch barrel with a perma AK break on it. He opened up the gas port for me and turned down the thickness of the barrel. The gas block is still the stock length but I can put a K grip on and have the vent poke out the front just like the C. His work if available through him or special weapons. I went through him and have not regreted it. I had a 2 week upper turn around and he took the thing back twice for service that turned out to be ammo - mag - gas hole combo problem that was easily fixed at no charge.
The black color of the furnature is easy to obtain with a 25 gallon bucket full of boiling water and a few bottles of RITs dye (I am not kiding I did my USC like this too.)
home.comcast.net/~kogashuk/g36o3.jpg